The present invention relates to a hose clamping structure in which a hose insertedly fitted to the outer surface of an inserting end portion of a metal pipe is clamped and secured to the metal pipe by tightening a sleeve member which is provided to cover the outer surface of the hose.
Conventionally, hose clamping structures of this type are classified into those for fuel hose having relatively low pressure-resistance (10 kgf/cm2) and those for power steering hose or freon hose having high pressure-resistance (100 kgf/cm2). In one exemplary hose clamping structure for a fuel hose, an adhesive agent is applied over the outer surface of a metal pipe; the resultant metal pipe and a rubber hose are adhered to each other; and a sleeve member mounted to the outer surface of the hose is tightened to a rubber hose in a flat tightening operation where the tightening section is tightened over a wide area substantially parallel to the axial direction. In another exemplary hose clamping structure for a fuel hose, an elastic member is interposed between a metal pipe and a rubber hose; for example, an elastic coating agent such as a rubber paste and the like is applied to the metal pipe; and a sleeve member is tightened onto a rubber hose at two portions in an axial direction in a two-stage tightening operation. In the case of a hose clamping structure for a power steering hose, ring-shaped grooves are formed in advance by a rolling process and the like at three portions of an inserting end portion of a metal pipe in an axial direction; a rubber hose is insertedly fitted to the metal pipe; a sleeve member is provided to cover the hose; and the sleeve member is tightened onto the rubber hose in a three-stage tightening operation at positions corresponding to the ring-shaped grooves of the metal pipe. As a result of employing the three-stage tightening operation, the clamping structure becomes too long for a fuel hose having low pressure-resistance, and layout of such clamping structure is difficult.
By the way, in the case where a clamping structure is used for connecting an automatic transmission with a radiator as is the case of the clamping structure for connecting an oil hose with a metal pipe in an automobile, oil having high temperature and high pressure flows through the clamping structure. For this reason, the hose clamping structure is required to have pressure-resistance of 25 kgf/cm2 or higher at high temperature, which is higher than the pressure-resistance of the hose clamping structure for the fuel hose. Further, in such a hose clamping structure, it is required that a portion tightened with a sleeve member has a length as small as possible due to the relationship with a location where the hose clamping structure is provided, and in addition, is required to be low in price. Considerations have been made as to what design of hose clamping structure is suitable for such an application. For example, in the above case of the hose clamping structure for a fuel hose, it is necessary to use an adhesive agent or a coating agent. This results in increasing the price of the connection structure. In addition, flat tightening operation cannot attain sufficient pressure-resistance and there is a possibility that a rubber hose may come off.
Contrary to the above, as shown in FIG. 3, it is possible to tighten the sleeve member in a two-stage tightening operation instead of flat tightening operation, without using an adhesive agent. The two-stage tightening operation is conducted by pressing a sleeve member 1 from eight directions on the circumference toward an axial center by use of a tightening dice 4 normally divided into eight segments in its circumferential direction and having projections 4a at opposite ends radially inwardly projected into a rectangular shape in cross section. However, in this hose clamping structure, a rubber hose 3 is clamped only at two ring-shaped tightening sections 2 of the sleeve member 1 in an axial direction. In this structure, the tightening force of the sleeve member 1 is not sufficient, and the hose clamping structure does not exhibit sufficient pressure-resistance at high temperature.
Further, in the hose clamping structure for a power steering hose, a rubber hose is insertedly fitted to a metal pipe, and a sleeve member is provided to cover the rubber hose. Then, the sleeve member is tightened in a three-stage tightening operation at positions corresponding to the ring-shaped grooves of the metal pipe. In this structure, it is possible to attain sufficiently high tightening strength without using an adhesive agent. If, however, a hose is long and has a curved portion, a large-sized pipe rolling apparatus is used. In this case, the production cost is increased, thereby increasing the price of the hose clamping structure. Further, since this hose clamping structure needs a three-stage tightening operation, the tightening portion becomes long. Accordingly, the hose clamping structure also becomes long, and there is a possibility that the layout thereof is limited when it is arranged.